How to make a higher jump? (767000)

Unity Engine
1

I would like my object to jump higher when I hold the button down. It can’t be a double jump, just a bigger jump power.
How to do it?
I tried to use bool to mark when the button is pressed, but it doesn’t make much sense.
I guess I should use Time, but I don’t know what to do here.
Can anyone help?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class PlayerBehaviour : MonoBehaviour
{
     public float moveSpeed;
     public float jumpPower = 1;
     private Rigidbody2D rb;
     public bool isGrounded = true;
     // Start is called before the first frame update
     void Start()
     {
         rb = GetComponent<Rigidbody2D>();  
     }
     // Update is called once per frame
     void Update()
     {
         rb.velocity = new Vector2 (moveSpeed, rb.velocity.y);
         if(Input.GetMouseButtonDown(0) && isGrounded)
         {
             //Jump
             rb.velocity = Vector2.up * jumpPower;
             isGrounded = false;
     }
     }
     void OnCollisionStay2D(Collision2D other)
     {
         if (other.collider.tag == "Ground")
         {
             isGrounded = true;
         }
     }
     void OnCollisionExit2D(Collision2D other)
     {
         if (other.collider.tag == "Ground")
         {
             isGrounded = false;
            }
}
}
2

I believe this video has the answers you need: